injury risk in harness racing horses

Hard tracks might have certain benefits when racing harness horses, such increasing internal structures’ loading rates. But new study results also showed a major increase in injury risk when training on hard surfaces compared to soft ones.

“We suspected harder surfaces led to more injuries, but we did not expect the rate to be so high,” said Nathalie Crevier-Denoix, DVM, PhD, Dipl. ACVSMR, of the Ecole Nationale Vétérinaire d’Alfort Equine Biomechanics and Musculoskeletal Pathology Department and the French National Institute of Agronomic Research.

In their pioneering study, Crevier-Denoix and her fellow researchers followed 12 3-year-old Standardbred racehorses of similar breeding and body shape over a four-month training program. Half the horses trained only on a hard track, and the other half trained only on a softer track. They worked three days a week for 16 weeks, except for the ninth week (in the middle of the training program) when they trained only once because they were undergoing various health exams in the clinic. Researchers also performed a complete clinical and imaging checkup at the beginning and end of the training program.

During each exam the researchers carried out extensive diagnostic imaging of the horses’ limbs to pick up early signs of damage to the bones, muscles, tendons, and ligaments, Crevier-Denoix said. They noted more serious lesions—and more lesions in general—in the hard-track group.

For example, 50% of the horses training on the hard track developed “marked to severe” superficial digital flexor tendon (SDFT) tendinopathy (tendon disease), she said. Two of these six horses became clinically lame and had to have their training programs reduced. In the soft track group, however, SDFT injuries were less common and less severe. They never reached a grade greater than 2 out of 4 and never caused clinical lameness.

Researchers found nine swelling-type lesions of the bone marrow in the 12 study horses’ 24 forefeet, Crevier-Denoix said, eight of which occurred in horses training on the hard surface. Similarly, the mean number of clinically relevant bone marrow lesions of the lower condyle of the hind cannon bone (the part of the cannon in the hind fetlock joint) was significantly greater in the hard surface group.

“Harder tracks mean greater speed, because the biomechanics are such that horses push off more easily than in a soft track,” she said. “Although in our study speed and distance were strictly controlled (identical in both groups), in real-life situations the increased speed observed on firmer surfaces, combined with increased maximal load and loading rate of the limbs during stance, as well as stronger vibrations within the limb at each impact, puts the musculoskeletal system at greater risk of injury.”

Crevier-Denoix noted that softer tracks can lead to push-off-related injuries, especially in the hind limbs, due to the greater strain of pushing against a less-resistant surface. But that injury risk is minor compared to the risk of always training on a hard surface, she said.

Training temporarily on hard surfaces can have some benefits, including increasing structures’ loading rate and ability, Crevier-Denoix added. “If a veterinarian recommends therapy by trotting on a harder surface, this can be useful, provided the speed is kept in check,” she said.

And racing on a firm track is not necessarily bad for the horse, either. “If they’ve trained on a soft surface and then get on a firmer (hard) surface, they’re going to go faster,” she said. “But we’re talking about one race that doesn’t last more than a few minutes. That’s not going to cause damage like four months of regular training on a hard surface.”

In this study, the most severe lesions occurred on the left legs—the inside leg as horses traveled counterclockwise around the track. Alternating directions could help prevent such overloading of a single limb, the researchers said.

Ideally, training should involve a mix of surfaces and directions, said Crevier-Denoix.

“And always remember to harrow and water down your tracks to keep them softer,” she said. “Watering is crucial.”

The study, “Effect of track surface firmness on the development of musculoskeletal injuries in French Trotters during four months of harness race training,” was published in the American Journal of Veterinary Research.